1. Field of the Invention
The invention relates to a new group of inorganic water-soluble polynucleate compounds containing at least two different metals, a trivalent metal and a divalent metal, where both the trivalent metal and the divalent metal form soluble salts with an associated divalent anion.
2. Description of Related Art
Aluminum sulfate has been the traditional chemical used in various water and wastewater treatment and paper processing applications. These include but are not limited to:
clarification of surface water to remove suspended solids, color and bacteria, making the water safe for human consumption or industrial use; PA1 clarification of municipal and industrial wastewaters to remove suspended solids, BOD, COD, phosphates and oils; PA1 retention of fibers and fillers in the production of paper; PA1 sizing of paper to make it hydrophobic; and PA1 control of pitch in the production of paper. PA1 M is a tri- or more valent metal ion, for example aluminum, iron, chromium or zirconium; PA1 N is a divalent metal ion that forms a soluble salt with anions X, Y or Z, for example magnesium, zinc or copper; PA1 OH represents the level of basicity; PA1 X is a monovalent anion, for example chloride, bromide, acetate or nitrate; PA1 Y is a divalent anion, for example as sulfate, selenate or oxalate; PA1 a is 1; PA1 b is from 0.15 to 2.0; PA1 c is from 0.3 to 5; PA1 d is from 0 to 3; PA1 e is from 0.1 to 2.25; PA1 f is from 0 to 1; and PA1 g is greater than 4 where the product is an aqueous solution, or from 0 to 20 where the product is not an aqueous solution.
Aluminum sulfate is generally produced by reacting alumina trihydrate (ATH)--Al.sub.2 O.sub.3.(3H.sub.2 O)--with sulfuric acid in an acid resistant digester. Bauxite containing gibbsite (Al.sub.2 O.sub.3.3H.sub.2 O) is also used as a low cost raw material for supply of aluminum sulfate.
Aluminum sulfate is normally supplied as a liquid solution containing 48.5% Al.sub.2 (SO.sub.4).sub.3.(14.3 H.sub.2 O). It may also be supplied as a dry product which is dissolved in water prior to use.
Ferric sulfate and other iron salts have begun to replace aluminum sulfate in many of the water and wastewater treatment applications, especially phosphate removal. Ferric sulfate reacts with suspended solids in a manner similar to aluminum sulfate but is generally less expensive. It is made by reacting ferric oxide with sulfuric acid; in several of the processes presently being used, pressure is needed to complete the reaction.
In the 1970's, a new class of inorganic polyelectrolytes started to replace aluminum sulfate. The first products that showed promise were poly aluminum sulfates. Processes for the production of poly aluminum sulfates are disclosed in U.S. Pat. Nos. 4,284,611 and 4,536,665 and Canadian Patents Nos. 1,123,306, 1,203,364, 1,203,664, and 1,203,665.
In these patents, poly aluminum sulfate is produced by reacting aluminum sulfate solutions with sodium carbonate or sodium hydroxide to form an insoluble aluminum hydroxide gel, and soluble sodium sulfate which is washed out of the gel. The gel is then redispersed in a fresh aluminum sulfate solution and reacted at elevated temperatures. The gel redissolves, basifying the aluminum sulfate making a poly aluminum sulfate (PAS).
These reactions may be summarized as follows: EQU Al.sub.2 (SO.sub.4).sub.3.(14.3H.sub.2 O)+6NaOH+42H.sub.2 O.fwdarw.2Al(OH).sub.3 +6Na.sup.+ +3SO.sub.4.sup.2- +56.3H.sub.2 O(IA) EQU 2Al.sub.2 (SO.sub.4).sub.3.(14.3H.sub.2 O)+2Al(OH).sub.3 +50H.sub.2 O.fwdarw.3Al.sub.2 (OH).sub.2.sup.4+ +6SO.sub.4.sup.2- +78.6H.sub.2 O(IB)
Poly aluminum sulfate solutions with basicities greater than about 15% made using this procedure have exhibited stability problems. Some of the solutions would be stable for several months where others were only stable for days. This stability problem was never resolved and this technology never reached full commercialization.
U.S. Pat. No. 4,877,597 describes another process for the production of poly aluminum sulfate. This process eliminated the initial step of producing an aluminum hydroxide gel by reacting aluminum sulfate with sodium aluminate: EQU 3Al.sub.2 (SO.sub.4).sub.3.(14.3H.sub.2 O)+2NaAl(OH).sub.4.sup.- +83H.sub.2 O.fwdarw.4Al.sub.2 (OH).sub.2.sup.4+ +2Na.sup.+ +9SO.sub.4.sup.2- +97.3H.sub.2 O (IIA)
This reaction results in the preparation of a 33% basic poly aluminum sulfate, although other basicities can be prepared using this procedure. This very reaction is sensitive to temperature, reaction and mixing conditions, and it is difficult to produce products that are stable above 33% basic. Basicities in the 20% to 25% range are more stable.
U.S. Pat. No. 3,544,476 discloses a process for formation of a poly aluminum chloro sulfate (PACS). It is prepared by first producing an aluminum chloride/aluminum sulfate solution and then basifying this solution with calcium carbonate or lime. PACS is formed and calcium sulfate precipitates. The insoluble calcium sulfate is removed, generating a clear, stable poly aluminum chloro sulfate solution with a basicity of 50% and an Al.sub.2 O.sub.3 concentration of 10%. EQU 18Al.sub.2 O.sub.3.(3H.sub.2 O)+33H.sub.2 SO.sub.4 +42HCl+867H.sub.2 O.fwdarw.11Al.sub.2 (SO.sub.4).sub.3 +14AlCl.sub.3 +975H.sub.2 O(IIIA) EQU 27Ca(OH).sub.2 +11Al.sub.2 (SO.sub.4).sub.3 +14AlCl.sub.3 +975H.sub.2 O.fwdarw.18Al.sub.2 (OH).sub.3.sup.3+ +42Cl.sup.- +6SO.sub.4.sup.2- +(27CaSO.sub.4.2H.sub.2 O+86H.sub.2 O).dwnarw.+835H.sub.2 O(IIIB)
This process produces a stable solution and the resulting product is an effective coagulant. PACS has proven its effectiveness by replacing alum in several applications.
U.S. Pat. Nos. 3,909,439 and 4,082,685 disclose a process for producing poly aluminum chloride (PAC). This process involves reacting alumina tryhydrate with hydrochloric acid under high temperature and pressure conditions. EQU Al.sub.2 O.sub.3.(3H.sub.2 O)+3HCl+42H.sub.2 O.fwdarw.Al2(OH).sub.3.sup.3+ +3Cl.sup.- +45H.sub.2 O (IVA)
This process produces a stable product at basicities up to 66% and Al.sub.2 O.sub.3 concentrations up to 18%. The most common product sold is 50% basic and 10% Al.sub.2 O.sub.3.
Another poly metal salt that has proven an effective product is aluminum chloro hydrate (ACH). It is prepared by reacting aluminum metal with either hydrochloric acid or aluminum chloride. EQU 5Al+AlCl.sub.3 +62H.sub.2 O.fwdarw.3Al.sub.2 (OH).sub.5.sup.+ +3Cl.sup.- +47H.sub.2 O+7.5H.sub.2 (gas) (VA)
This process produces a stable product at basicities up to 83% and Al.sub.2 O.sub.3 concentrations up to 24%. The most common product sold is 70% basic at 23% Al.sub.2 O.sub.3.
U.S. Pat. Nos. 4,981,675, 5,069,893, and 5,149,400 disclose various processes for producing poly aluminum silica sulfate (PASS). In these processes, aluminum sulfate is reacted with an alkali metal silicate and alkali aluminate in an aqueous solution under high shear mixing conditions. The following reaction is typical: EQU 1.25Al.sub.2 (SO.sub.4).sub.3 +0.0062(Na.sub.2 O.0.322SiO.sub.2)+0.75Na.sub.2 Al.sub.2 O.sub.4 +3H.sub.2 O.fwdarw.4Al(OH).sub.1.50 (SO.sub.4).sub.0.735 (SiO.sub.2.131).sub.0.05 +0.812Na.sub.2 SO.sub.4 (VIA)
Products made using this reaction generally have a basicity of 50% and an Al.sub.2 O.sub.3 equivalent concentration of 8.3%, althought products with basicities ranging from 25% to 66% can be made using this technology.